The present invention relates to devices for muscle stimulation, in particular devices which employ safety mechanisms to prevent overstimulation in case of user error or system failure.
It has been found that scoliosis can be treated by electronic muscle stimulating devices. In one class of devices, electrodes are implanted to act upon muscles along the sides of the spine. An RF receiver is implanted to power the electrodes. When treatment is to be administered, an RF transmitter is placed over the receiver to drive the electrodes. For a general discussion of such treatment of scoliosis see "Electrospinal Instrumentation for Scoliosis: Current Status," by Bobeschko, Herbert and Friedman, Orthopedic Clinics of North America, Vol. X, No. 4, October, 1979. U.S. Pat. No. 4,026,301 to Friedman et al discloses apparatus and method for treating scoliosis with implanted electrodes. Other devices treat scoliosis transcutaneously through skin-mounted electrodes.
Treatment of scoliosis patients with such a device is usually accomplished during the night while a patient is sleeping. Therefore, the stimulator or transmitter, wires and other external apparatus are not used during the day time hours, which prevents embarrassment to the patient.
If the patient is sleeping during treatment, instantaneous changes in the treatment cannot be immediately recognized by the patient. Normally the treatment consists of short periods of electrical stimulation followed by a longer period of rest. This continues throughout the night. For example, a cycle might contain a five second burst of stimulation followed by a twenty-five second rest period. Should parts of the equipment malfunction, and the duration of the stimulation phase extend too long, irritation to the patient's muscles may result. If, for example, constant stimulation occurred, the patient would eventually wake up, but soreness of the back might result.
While failures of such circuitry have not been clinically observed, in a product where a patient's health is concerned it is imperative to take all possible precautions in preventing possible equipment failures from irritating the patient.
Some such stimulation devices include a constant stimulation button, which can be activated by the patient to obtain a steady stream of stimulation. To ensure that such a constant stimulation button is not misused, or that the user does not activate it for an improperly extended period, it is desirable that the stimulator be designed to deactivate before the constant stimulation can have undesirable medical effects.
An example of a previous muscle stimulator which may be used in the treatment of scoliosis is disclosed in U.S. Pat. No. 4,392,496 by David J. Stanton, issued July 12, 1983. Part of the circuitry disclosed in this application is disclosed and claimed in that application.